1. Field of the Invention
The present invention relates generally to a wavefront sensor for detecting wavefront tilts, and more particularly pertains to a wavefront sensor of the aforementioned type utilizing a surface acoustic wave generator which produces a reflecting diffraction grating by surface deformations induced by acoustic waves in a solid medium.
Wavefront sensors have particular utility in the field of active optics for sensing the distortion of an optical wavefront from a desired wavefront shape such as a plane or spherical wavefront. The field of active optics technology can be applied to high performance optical systems which encounter or are subject to random disturbances such as vibration, thermal transients or atmospheric turbulence, such as laser beam control systems and compensated imaging systems. In greater detail, the wavefront sensor of the present invention was designed as a diagnostic tool for a laser beam which can be considered to be essentially a point source of monochromatic radiation.
2. Discussion of the Prior Art
Wyant U.S. Pat. No. 3,829,219 is considered to be somewhat pertinent to the present invention as this patent is also concerned with a wavefront sensor for detecting the shape of a wavefront surface by the utilization of an AC shearing interferometer. In a greater detail, this patent discloses a shearing interferometer for producing a shearing interferogram of a wavefront being converged to a focal point in which two diffraction gratings having slightly different frequency line spacings are placed near the focal point of the wavefront. The diffraction gratings produce two first diffraction orders at two slightly different angles, which results in a shearing interferogram being generated in the region of overlap. The resulting shearing interferogram yields wavefront information in one direction. Complete wavefront information in two directions is obtained by shearing the wavefront in two orthogonal directions by placing two additional diffraction gratings having slightly different frequency line spacings near the focal point of the wavefront in an orthogonal direction relative to the first two diffraction gratings. The interferometer may use heterodyning, real time phase detection in which the irradiance of the interferogram is modulated sinusoidally by translating sideways at least one of the diffraction gratings.
Although this patent is similar in some respects to the present invention, it is quite different in several important aspects. The patented system utilizes transmissive, as opposed to reflective, diffraction gratings, and also the transmissive diffraction gratings require a mechanical oscillating drive for the gratings, such as an electromagnetic moving coil drive.